Last year, Apple surprised developers and analysts alike by debuting a preview of OS X Mountain Lion, then announcing it was shifting to an annual release schedule for its Mac operating system.

That was Feb. 16, 2012, a year and three weeks ago.

So where is OS X "Next," or whatever name Apple chooses for its latest operating system?

If Apple is on the same schedule as last yearand the year before that -- a preview in February, a July ship date -- the company is running behind. In 2012, Apple offered registered developers their first look at OS X Mountain Lion on Feb. 16, then 161 days later shipped the upgrade. 2011's schedule was similar, but with 147 days between OS X Lion's developer preview and release.

Assuming Apple announced a preview of OS X today and stuck to those time lines, the upgrade would be released between Aug. 5 and Aug. 19.

That's later than the last two years, but within the "annual" cadence, according to one analyst. A year ago, Michael Gartenberg of Gartner Research, who was told by Apple that it was putting OS X on an annual pace, said, "There may be a month here or a month there," of flexibility in the schedule.

Gartenberg's take, as well as the timetables for the last two iterations, suggests that Apple will be releasing a preview of OS X Next soon, perhaps in the next few weeks.

Speaking of "Next," the naming of OS X 10.9, as the upgrade would be numbered, remains a mystery. Although some Apple enthusiast blogs speculated last fall that it could be designated "Lynx" or "Cougar" -- two of the trademarks Apple registered in 2003, along with the already-used "Tiger" and "Leopard" -- neither may be available.

Apple's Lynx trademark was designated "abandoned" in Dec. 2007, while Cougar met the same fate in May 2008. In both cases, according to the U.S. Patent and Trademark Office, the trademarks were dumped because Apple failed to file an extension in a timely fashion.

The faster release pace will further fragment Apple's operating system as new editions are launched while older ones remain in widespread use.

According to online metrics company Net Applications, there are now four editions -- 2007's Leopard, 2009's Snow Leopard, 2011's Lion and 2012's Mountain Lion -- with a 7% or great usage share of all Macs.

That won't change much by summer: Projections based on Net Applications' data indicate that at the end of July, Snow Leopard and Lion will still power about one in five Macs each, while Mountain Lion will account for half of all Macs.

Because Apple's support policy is muddied -- it does not spell out how long it continues to patch an OS X edition -- the faster cadence will either require it to simultaneously support more operating systems, or cut short support of editions used by millions. Either would be a marked departure for the company.

Apple has already reached that point because of the two back-to-back releases of Lion and Mountain Lion. Previously, Apple patched only "N" and "N-1," where N was the newest edition, and halted support for N-2 about the time it shipped N. Instead, Apple patched Snow Leopard last fall, months after Mountain Lion's launch, and may again in the coming weeks, when the company is expected to upgrade Mountain Lion to 10.8.3, and patch Lion.

Come July or August and the debut of OS X Next, Apple may be forced to keep patching Snow Leopard -- at that point it would be N-3 -- because Snow Leopard will still account for approximately 23% of all Macs.

Microsoft will face the same issues if, as rumors have hinted, it quickens the release cadence for Windows by also shifting to an annual schedule. The first such upgrade -- or update, since its extent is still unclear -- has been designated "Blue" by bloggers, who claim that it will appear this summer.

Apple's practice is to reveal its newest OS X at the company's annual Worldwide Developers Conference (WWDC), which is held in San Francisco in June. It starts selling the upgrade several weeks later, probably via only the Mac App Store, like last year, and at the same $19.99 price.

According to the current schedule of the Moscone Center, where Apple has hosted WWDC since 2003, the week of June 10-14 is the only five-day stretch starting with a Monday that is not already booked. If that is the week of WWDC -- which Apple has yet to announce -- it would unveil OS X Next during the opening keynote on June 10.